Pressure leaf filters are well known for use, for example, in the beverage industry to eliminate tiny particles of matter. The liquid to be filtered is introduced, under substantial pressure, into large pressure tanks containing multiple filter leaf elements. The pressure drives the liquid from the exterior of the filter leaf elements to their interior, from which it flows through a common manifold to the exterior. Such filtering systems are available from numerous sources, such as the Duriron Company of Angola, New York. Filter leaf elements of varying design are available from sources as the Duriron Company of Albany, N.Y., as well as the Lenser Company of Germany.
At least two types of pressure leaf filter element constructions are known. One type, of welded stainless steel construction, includes a filtering screen through which liquid is pumped, the screen conventionally bearing a covering of diatomaceous earth. The filtering screen on the outer side of the leaf may be supported inwardly by a succession of coarser screens or perforated plates through which the screened liquid is drained. These leaf elements are typically costly, heavy, and not easily repaired if their filtering screens are damaged. Another known pressure filter leaf construction uses a fabric bag loosely enclosing a polypropylene element molded with parallel grooves perforated to lead to a hollow interior from which the liquid, screened by the fabric of the bag, is drained through a common outlet. As a disadvantage, if the bag is loose, inflow pressure may press the weave into the groove of the plastic leaf element, whereas if the bag is tight, the weave may be distorted enlargingly in either case defeating its intended function as a precise screen.